Process of producing sensitive silver halide-colloidal aggregates



Dec. 15, 1942. F. LIERG 2,305,169

PROCESS OF PRODUCING SENSITIVE SILVER HALIDE-COLLOIDAL AGGRGATES Filed March '7, 1938 Patented bec. 15, 1942 s PATENT OFFICE PROCESS F PRODUCING SENSITIVE SILVER HALIDE-COLLOIDAL AGGRE- GATES Friedrich Lierg, Vienna, Austria; vested in the Alien Property Custodian Application March "l, 1938, Serial No. 194,469.

In Austria March 16, 1937 4 Claims.

Sensitive silver halide emulsions are produced practically exclusively by gelatine solutions, -al though attempts have been made to substitute another colloid as carrying and protecting colloid for the silver halide for the gelatine, which is not of uniform nature and therefore varyingly influences the preparation of the silver halide emulsion.

In view of the progress in the manufacture of I cellulose films, especially in view of the production of cellulose hydrate illm, known by the name cellophane films, attempts have been made to use these or similar cellulose hydrate productions as carrier of the sensitive silver halide. All corresponding processes and patents make use of the water absorbing capacity of the cellulose hydrate layers in order to precipitate the silver halide within the cellulose hydrate layer by the successive imbibition of the components forming the silver halide.

Contrary to all known processes, in the process according to the present invention the addition of the silver halide to the carrier colloid is carrid out in accordance with certain rules and precriptions determined in accordance with the latter in order to produce sensitive i'llms without layer, so that silver halide colloid aggregates exactly of the desired sensitiveness and characteristic of graduation are produced. In the process according to the present invention use is made of the colloid-chemical nature of the carrier colloid as well as of the silver halide in its nascent state, e. g. differently from all known processes it places in reaction the carrier colloid when forming the silver halide in the carrier colloid by utilising-its electropolarity and that of the silver halide in the nascent state or by artificially producing the same.

According to the present invention the following rules have to be followed during the silver halide precipitation within the carrier colloid for the systematic constitution of a sensitive silver halide colloid aggregate of exactly determined characteristics.

If a cellulose hydrate layer, produced for instance from an acetyl lm by alkaline saponiflcation, is imbibed with a silver nitrate solution and if after its desiccation it is treated in the dark in a solution of bromides, there will take place silver bromide precipitations within the cellulose hydrate layer as carrier colloid, just in the same way as if a solution of bromides is used as rst imbibition bath andhereafter treatment is effected in the silver nitrate bath, whereby the quantity of the silver bromide introduced development-proof in the unexposed condition as well as its other characteristics depend on the electropolaric characteristic of the carrier colloid. Thereby the silver bromide can be introduced only under certain conditions, which will be described hereinafter. That silver bromide, which has been formed by the flrst imbibition. of the silver nitrate solution and the subsequent treatment in a solution of 'bromides, always showed a very small sensitiveness, which reminded one of the sensitiveness of a Lippmann silver bromide emulsion, while the silver bromide produced by the treatment in a solution of bromides and the subsequent treatment in a silver salt bath is considerably darker in colour although it is'imbibed quite transparently and is very sensitive. As mentioned, the carrier colloid was of considerable influence even after the silver bromide substitution because. if the saponication of the acetyl cellulose is effected slowly by means of diluted potassium hydroxide, the saponifled layer is not very capable of absorbing silver bromide which is development-proof (i. e. proof against blackening by a developer in non-actinic light). e. g. which is combined with the carrier colloid, as it will be explained hereinafter, while considerable quantities of development-proof silver bromide could be introduced in the event of concentrated saponication potassium hydroxide, which needs a short duration of action until the same degree of saponication is reached. The phenomenon involved is believed to be a case of a colloid-chemical polarity.

If the silver bromide is produced in the disacetylated acetyl cellulose by subsequent treatment in a solution of silver salt, e. g. if by the presence of the silver salt in excess the silver bromide is charged positively which in the nascent state always is of colloidal nature, the negative diacetylated acetyl cellulose does not react as a protective colloid, but an electrosorption takes place in view of the compensation of the opposite charges. By the expression electrosorption it is to be understood the combination of two colloids of opposite electric charges. As is known, this compensation of opposite charges leads to coagulation in the case of liquid colloids which,

gelatine emulsion; the only technically important difference being, that the silver bromide substituted in the diacetylated acetyl cellulose resu1ts,

after its exposure and development in spite of its sensitivity, in grainless silver images while, as is known, the sensitive gelatine silver bromide promoted by ripening results in coarse grained silver images. lhe precipitation of two oppositely charged colloidal substances results, as is known, in a total discharge incase of a certain proportion of quantities. If the one or the other colloid is present in excess a residual charge remains'which, in the event oi' a considerable excess, may be so large that the precipitation does not take place. By means of substances, which are capable of reducing this residual charge, for instance by admixture or the subsequent treatment with certain dyes, it is possible to increase the sensitiveness and finally to cause total fogging, if the residualcharge becomes too small to impart the aggregate with the necessary stableness against development substances, e. g. development-proofness. A bathing of the highly sensitive silver bromide colloid aggregate even in a. very diluted potassium bromide solution very considerably reduces the said sensitiveness to such an extent that, according to the introduction of the potassium bromide solution, the latent image finally disappears entirely from the nlm-surface. This renders the electro-polarized nature of the halide silver-colloid aggregate quite clear and also its diierentiating pecularity compared with a silver bromide gelatine emulsion.

In principle, Cellophane shows the same characteristics as disacetylated acetyl cellulose but somewhat weaker which isquite obvious, because the regeneration of the cellulose from all` its esters (nitrofacetylxanthate) results in hydrate cellulose which, per se, embodies already .a structural negative polarity owing to the free OH groups present in the molecule.

After all these experiments it has been shown that now the above mentioned developmentproofness of the bromic silver, introduced in the carrier-colloid in darkness, depends upon the fact that the same is combined in its nascent state with the carrier-colloid and that thereby the silver bromide is prevented from bolling together and thereby losing its development-proofness. Thus the directions have been given for an absolutely development-proof and fog-free bromic silver addition to the carrier-colloid. In order to produce the desired effect it is necessary to select or try the concentrations of both reagents of the silver bromide formation, the bromide and the silver salt solution according to the succession of the baths and in proportions of concentration, so that either in view of its protective eiect or of its electrosorption, the formed silver image is added faster to the colloid, than corresponds to the rate at which the silver bromide balls together. Thereby care has Vto be taken to prevent that, for instance by diiusion of the first imbibed bromides, more silver bromide is formed towards the silver nitrate bath in the surface zones, than the hydrate cellulose can x in view of its charge, because an excess thus produced causes also in the unexposed state a fogging during the development for want of combination with colloid-particles. This elimination by diffusion canbe counteracted and also the above mentioned conditions of imbibition can be satisfied in accordance with the present process if the suitable solvents for the salts to be imbibed are used and iftheir dissolving characteristics in the same are suited by the selection of convenient soluble and insoluble salts; if desired also damping agents may be added. The elimination by diffusion of the rst imbibed bromide in the after-bath of silver nitrate may be prevented by addition thereto a large quantity of alcohol and using for the rst imbibition a bromide, for instance cadmium bromide, which is diiiicultly soluble in methyl alcohol. Organic halogen compounds. which are capable, with silver salt, of

forming silver halide, can also be employed in place of the hereinbefore mentioned inorganic water-soluble halogen compounds. I'hese organic halogen compounds are preferably employed in a form having the maximum resistance to solution in water, and, being dissolved in organic solvents such as alcohol or the like, are imbibed in the cellulose-hydrate layer. In order that the halogen salt which has been absorbed into the layer and which has been dried therein, shall not again be dissolved out in the subsequent bath of the silver salt, the silver nitrate is in this instance employed ina solution of nothing but water.

Instead of the potassium bromide or other 'inorganic halogen-salt solution there may also, as already stated, be employed organic halogen-salt solutions, particularly those whose water-solubility diiers from that of the silver salts, and which are therefore imbibed, by means of a volatile organic solvent, in the deacetylated acetyl cellulose.

Thus from this results also those reagent additions for the prescription, which are of advantage for the development-proof imbibition of silver bromide as well as for determining their sensitiveness in accordance 'with the process. Thus for instance an addition of ammonia in certain proportions with respect to the silver salt bath causes the increase of the negatively polarized charge of the cellulose hydrate and arrests the rapid balling together oi the silver bromide and facilitates the rapid introduction of the silver bath into the hydrate cellulose by enhancing the capacity of swelling and wetting. Any necessary additions such as for instance iodides, alkaline earths salts and so forth may be added to the bromine-bath.

The knowledge of the procedure of the reaction renders possible, besides the optimum state of the prescription for the substitution of silver bromide in convenient colloids also that correct steps may be taken for adapting also colloids, which do not possess any or a little qualification only, for the substitution of silver bromide which is development-proof in the unexposed state. This may be done for instance by the deesterication in such a way, that a desired degree of polarity is produced or that, for the same object, substances are introduced into the colloid, which iniiuence its polarity in the desired manner.

Thus the feature of the present invention il view of the exact knowledge of the colloidchem ical procedure taking place during the addition of silver halide to rigid colloids, renders it possible to place in reaction the carrier-colloid by the suitable selection of its polarized characteristic either artificially produced or influenced by convenient additions, just like the polarized characteristic of the silver halide may be determined by prescribed measures during its precipitation, so that by the precise selection of both polarities it is possible to obtain the carrier-colloid adapted to the exact characteristics of an exactly con.. ducted electrosorption of the halide silver and that in this way are added to the carrier-colloid not only fog-free and development-proof silver bromide, but also the desired sensitiveness and the characteristic 'of the finally obtained silver image, also with respect to its graduation and the like, can be determined and produced ver-colloid aggregate.

Eample An acetyl cellulose film is saponified in a bath of 1 part in volume of potassium hydroxide of 40 B., 1/2 part in volume of alcohol and 2 parts in volume of Water, hereafter the same is well washed for minutes. Now the film is dipped into a potassium bromide solution of 10%, the excess is drained off and dried. Instead of potassium bromide, also bromides which are of different solubility with respect to the silver salt may be added to the deacetylated acetyl cellulose. If necessary, the halogen salt after drying may be homogenised in a steam chamber. Hereafter the saponiiied acetyl cellulose impregnated with potassium bromide is immersed in a silver bath in the dark, that is to say, as photographers will know, in non-actinic light, which consists of a silver nitrate solution of 7.5% to which are added, for every 100 cc., 13.5 ccm. ammonia (specific Weight 0.91) and 200 to 500 cc. of methyl alcohol. This mixture will be recognized by chemists as an alcoholic solution of ammoniacal silver nitrate, and reference to any chemical handbook containing tables of solubility will disclose that potassium bromide is only slightly soluble in alcohol. After the treatment in this solution of approximately one minute, the film thus prepared is washed for 2 hours.

Contrary to the silvered collodion-coated plate of the so-called Wet collodion process, the silver halide colloid aggregates produced in the manner hereinbefore described may be treated in the dry condition without that fogging, decomposition, insufficient absorption of the developer and like drawbacks may arise.

When used in practice for instance in the graphic art, in which the production of grainless screen-lined silver images in large-surfaced projected enlargements on quite flat material is of special importance the lm silver halide colsurfaces having layers I2, I2 which have been transformed into cellulose hydrate and impregnated in the same manner. 1

In Fig. 4, 4a coat I0 of cellulose hydrate as shown in Fig. l is applied to a rigid or flexible carrier I3 of any convenient material.

Fig. 5 illustrates a rigid or flexible carrier I3 of any convenient material, provided with a cellulose ester coat Il, and a hydrate layer I2 as shown in Fig. 2, the layer I2 being impregnated with a silver halide.

What I claim is:

1. A process of producing a sensitive grainless silver bromide layer, proof againstl blackening by a photographic developer in non-actinic light, which process comprises in subjecting at least one surface of an acetyl cellulose lm to a bath comprising by volume:

until it is at least supercially saponified, then ywashing the nlm, then impregnating the saponiloids may be applied in thin layers to any convenient base. For this object, the acetyl cellulose may be spread or sprayed onto the desired base in the nature of a liquid cellone varnish and may be deacetylated after drying and the silver bromide may be substituted; or from the outlet, thin sensitive silver bromide Cellophane sheets are produced which are applied to plate-glass or metal plates which', owing to the said pressure and heatresistance of the sensitive silver bromide cellulose hydrate, may be effected by calendering in a dry or warm state by 'means of a fusing agent.

Some modes of carrying out the present in- ,vention are illustrated by way of example and Adrate in a layer I2 by the treatment with alkalis.

Grainless silver halide is introduced by electrosorption into the transformed surface layer, the halide being indicated by the stippling.

Fig. 3 shows a. cellulose ester sheet Il, both ed portion with potassium bromide by immersing it in a ten per cent solution of that salt, then draining and drying the film and subjecting it to a bath having the following proportionate composition: i

Cc. Silver nitrate (7.5% aqueous solution) Ammonia solution (0.91 specific gravity) 13. 5 Methyl alcohol 200 to 500 until the potassium bromide has become silver bromide, finally washing and drying the film, the

treatment with silver nitrate and subsequent parts water, well washing the lm, hereafter dipping the film into a potassium bromide solution of about 10%, draining and drying the film, subsequently bathing the film for about 1 minute in a silver nitrate solution of about 7.5% to which are added for every 100 ccm. 13.5 ccm. ammonia (specific weight 0.91) and 200 to 500 c. c. of methyl alcohol, and finally washing the film.

3. A process of producing photographic films by successively impregnating the carrier colloid with halogen salts and silver salts, consisting in impregnating a cellulose hydrate lm with water soluble inorganic halides, drying the lm and then treating the film with a. silver nitrate bath containing at least a double quantity of an organic solvent in which the inorganic halogen compound employed is difllcultly soluble in order to obtain a complete formation of the silver halide Within the film or layer.

4. A process of producing photographic films by successively impregnating the carrier colloid with halogenV salts and silver salts, consisting in impregnating a cellulose hydrate film with Water soluble inorganic halide selected from the group consisting of cadmium bromide and zinc bromide which is adsorptively. combined with the cellulosehydrate film, drying the nlm and treating the film with a silver salt bath containing at least a double quantity of an organic solvent for completing formation of the silver halide within the nlm or layer.

` FRIEDRICH LIERG. 

